1. Field of the Invention
In injectors that serve to inject a well-measured quantity of fuel, which is under extremely high pressure, into combustion chambers of internal combustion engines, leaking oil slides are embodied on the leaking oil side in the control parts supported displaceably in the injector housing; these slides require precise guidance in the housing. The precise guidance of the leaking oil slides in the housing of the injector demands high-precision manufacture, if a satisfactory sealing on the leaking oil side is to be achieved. Furthermore, with leaking oil slides embodied on control parts, short overlaps occur. As operating pressures increase more and more, especially in applications of the injectors in conjunction with high-pressure collection chambers (common rail), the injectors and their components must withstand the high pressures that occur.
2. Description of the Prior Art
German patent disclosure DE 198 35 494 A1 relates to a unit fuel injector used to deliver fuel to a combustion chamber of direct-injection internal combustion engines. The pump unit accomplishes the buildup of an injection pressure and serves to inject the fuel into the combustion chamber via an injection nozzle, and it has a control unit with a control valve. The control valve is embodied as an outward-opening valve. A valve actuation unit is also present for controlling the pressure buildup in the pump unit. To create a unit fuel injector with a control unit that is simple in design, small in size, and in particular has a short response time, it is proposed that the valve actuation unit is embodied as a piezoelectric actuator, which has substantially shorter response times than an electromagnet, for instance.
German patent DE 37 28 817 C2 relates to a fuel injection pump for an internal combustion engine which includes a control valve member comprising a valve shaft that forms a guide sleeve and slides in a conduit and a valve head connected to the shaft and oriented toward the actuation direction. Its sealing face cooperates with the face of the control bore that forms the valve seat, and the valve shaft has a recess on its circumference. The axial length of the recess extends from the orifice of the fuel delivery line to the beginning of the sealing face at the valve head that cooperates with the valve seat. In the recess, a face exposed to the pressure of the fuel delivery line is formed, which is equal in area to a face of the valve head that in the closed state of the control valve is exposed to the pressure of the fuel delivery line. As a result, in the closed state of the valve, a pressure-balanced state ensues, and a spring element that urges the control valve to its open position is received in the guide sleeve.
The use of spherically configured closing elements in injector housings of injectors for injecting fuel at high pressure both as valve elements on the leaking oil side and as control parts for opening and closing the nozzle inlet makes short stroke paths possible. Spherically configured valve control bodies are DIN components and are quite economical components that can be procured in micrometer diameter graduations and are therefore available as spare parts in arbitrary installation sizes. Because of their geometrical shape, they withstand the highest pressures and they are machined with the highest surface quality.
If a spherical valve control element is used on the leaking oil side as a leaking oil valve instead of a leaking oil slide, then minimal stroke paths can be realized; this markedly shortens the phase during which the inlet to the high-pressure collection chamber (common rail) is not yet closed, yet the leaking oil outlet has already been opened for pressure relief of the injection nozzle. This overlap in the opening phases can advantageously be varied by providing that the valve stroke h1 of the control part, embodied for instance as a control piston, is longer than the leaking oil valve stroke h2 that is established at the spherical closing element. This can be achieved by a suitably dimensioned spring element, which can be let into the valve body. By a suitable support of the spherical closing element on a pressure bolt provided in stationary fashion in the injector housing, the control part can be moved vertically up and down relative to the spherical closing element that is acted upon by a prestressing element. In its use, with the spring-urged spherical valve control body acting as a seat valve, significant advantages with regard to the stroke paths can be obtained, compared with variant embodiments of leaking oil slides and control parts.
When a spherical seat valve, which can be acted upon by a stepped piston serving as a control part, is used, DIN balls can also be used as the valve body; these are made in micrometer graduations and are economical components. When a spherical control body is used, the control part can be embodied in two parts, which has advantages in terms of the positioning of the leaking oil outlet that is provided for pressure relief of the injection nozzle. Upon pressure relief of the control chamber, which is supplied, through an inlet throttle associated with it, with fuel at high pressure acting as a control volume, precise metering of the injection quantity to be injected can be specified at the spherically embodied control body, as a seat valve, with a minimum stroke path, and this injection quantity enters the nozzle chamber surrounding the nozzle needle through the nozzle inlet.
When a stepped control body is used to act on the spherical valve body, one diameter graduation of this essentially rotationally symmetrically embodied component can certainly be used as a leaking oil control slide, since in the present case that part is especially simple to produce from a manufacturing standpoint.